Although various agricultural and horticultural antimicrobial agents (plant disease control agents) have been conventionally known, a more effective agent which can be more safely used is needed.
In such circumstance, Bacillus sp. bacterium is known to produce antimicrobial secondary metabolites. Among the antimicrobial secondary metabolites, cyclic peptide of the iturin class is the most important (Non-patent documents 1 and 2).
The cyclic peptide of the iturin class is a cyclic peptide having seven α-amino acids and one β-amino acid having an aliphatic side chain, and various compounds having different amino acid sequences and the structures of the side chain of β-amino acid (β-AA) have been reported. The structures of the iturin family having such a structure are shown in Table 1.
TABLE 1
The structure of iturin A was reported by F. Peypoux et al. in 1978 (non-patent document 3), and the structure was reviewed by A. Isogai et al. in 1982 to determine the structure of Iturins A1 to A7 comprising β-amino acids having a side chain structures of n-C13, n-C14, ai-C15, i-C15, n-C15, i-C16 and n-C16 (n=normal; i=iso; ai=anteiso; the same shall apply hereinafter) (non-patent document 4). In the report, iturin comprising β-amino acid having a side chain of C14 and C15 accounts for a majority. However, G. Winkelman et al. reported iturin AL comprising β-amino acid having a side chain structure of C15 and C16 and showed that the component ratio of the side chain structure of β-amino acid is different depending on the strains (non-patent document 5). Furthermore, S. Hiradate et al. reported in 2002 the structure of Iturin A8 comprising β-amino acid having a side chain of ai-C17 from B. amyloliquefaciens RC-2, and all the structures of
Iturins A1 to A8 were elucidated (non-patent document 6).
Mycosubtilin was discovered by R. Walton et al. in 1949 (non-patent document 7), and the structure comprising β-amino acid having side chains of n-C16, i-C16, i-C17 and ai-C17 and seven α-amino acids was determined by F. Peypoux et al. in 1986 (non-patent document 8).
Bacillomycin F was isolated from B. subtilis by A. Mhammedi et al. in 1982 (non-patent document 9), and the structure comprising β-amino acid having side chains of i-C16, i-C17 and ai-C17 and seven α-amino acids was determined by F. Peypoux et al. in 1985 (non-patent document 10).
Bacillopeptin was isolated by Y. Kajimura et al. in 1995 and the structure comprising β-amino acid having side chains of n-C14, i-C15 and i-C16 and seven α-amino acids was reported (non-patent document 11).
Bacillomycin Lc was isolated from B. subtilis by M. Eshita et al. in 1995 and the structure comprising β-amino acid having side chains of n-C14, ai-C15, i-C15, i-C16 and n-C16 and seven a-amino acids (the same sequence as that of Bacillopeptin) was elucidated (non-patent document 12).
Bacillomycin L was isolated from B. subtilis by M. Landy et al. in 1984 (non-patent document 13) and the structure comprising β-amino acid having side chains of n-C14, ai-C15, i-C15, i-C16 and n-C16 and seven α-amino acids was proposed by F. Peypoux et al. in 1984 (non-patent document 14). However, later, in 2007, the structure of α-amino acid was revised by L. Volpon et al. and it was revealed that Bacillomycin L has the same structure as Bacillomycin Lc (non-patent document 15).
Bacillomycin D was discovered by F. Raubitschek et al. in 1950 (non-patent document 16), and later, in 1981, the structure was once proposed by F. Peypoux et al. (non-patent document 17). In 1984, the structure was revised by F. Peypoux et al. to the one comprising β-amino acid having side chains of n-C14, ai-C15, i-C15, i-C16 and n-C16, two-molecule Asn and one molecule each of Tyr, Glu, Pro, Ser and Thr (non-patent document 14). In the report, β-amino acid has the component ratio of n-C14=47.6%, i-C15=22.7%, ai-C15=12.5%, i-C16=3.3% and n-C16=8.8%, in which Bacillomycin D comprising β-amino acids of C14 and C15 is the major component. In 2005, G. K. Oleinikova et al. isolated i-C15 Bacillomycin D from marine B. subtilis and determined the structure (non-patent document 18).
In 2001, A. C. Moyne et al. isolated two components having activity on Aspergillus flavus from B. subtilis and presumed the substances to be C15- and C16-Bacillomycin D (non-patent document 19 and patent document 1). In 2011, O. Tabbene et al. isolated from B. subtilis three active substances having antimicrobial effect on Candida albicans which is pathogenic to humans, and considered that these substances are C14-, C15- and C16-bacillomycin D by MALD f TOF/MS analysis (non-patent document 20). In 2004, A. Koumoutsi et al. presumed that C14, C15, C16 and a very small amount of C17 Bacillomycin D are present by the MALDI-TOF/MS analysis of the culture of B. amiloliquefaciens FZB42, but had no mention on the structure of the side chain of β-amino acid (non-patent document 21 and patent document 2). In 2007, R. Ramarathnam et al. analyzed the antimicrobial component of B. subutilis 49 strain by MALDI-TOF/MS and presumed the component to be Bacillomycin D containing a very small amount of C17 Bacillomycin D, but had no mention on the detailed structure of Bacillomycin D (non-patent document 22).
Meanwhile, there has been a report on the correlation between the structure and activity of cyclic peptide of the iturin class as set forth below. In 1993, J. M. Bland et al. studied on the structure of Iturin A and its activity on Penicillium and Aspergillus and reported the relationship of i-C16>n-C16>i-C15>n-C14=ai-C15 (non-patent document 23). Also, in 1995, M. Eshita et al. investigated the in-vitro activity of Bacillomycin Lc against the plant pathogens and revealed the relationships of n-C16>n-C14, i-C16>i-C15, n-C16≥i-C16 and i-C15≥ai-C15 (non-patent document 12). However, they had no mention on the activity of cyclic peptide of the iturin class having a C17 side chain.